Coding method for moving picture

ABSTRACT

The present invention relates to a method for coding a moving picture in a moving picture coding system using multiple reference picture. According to the method for coding an interlaced moving picture into a frame picture having frame/field macroblock, a reference picture index of the frame macroblock is determined at a macroblock level by determining the reference picture index of frame unit at a picture (or slice) level and respectively allocating a lower index and a higher index to a top reference field and a bottom reference field while sequentially visiting the reference frames according to an order of reference picture index of frame unit, the top and bottom field indexes being giving by an equation: top reference field index=2×picture index of reference frame; and bottom reference field index=2×picture index of reference frame+1.

TECHNICAL FIELD

The present invention relates to a method for coding a moving picture,and more particularly, to a method for coding interlaced moving pictureinto frame picture having frame/field macroblock in a moving picturecoding system that uses multiple reference pictures.

BACKGROUND ART

Moving picture coding system compensates for motion using motion vectorinformation. In case of moving picture coding system that uses multiplereference picture, reference picture index information as well as motionvector information is required for motion compensation. The referencepicture index is a value that is used to distinguish multiple referencepictures from each other. A coder transfers the reference picture indexto a decoder, and the decoder performs motion compensation fromreference picture that is indicated by the reference picture index.

Generally, scanning methods are classified into a progressive scanningand an interlaced scanning. In case of the progressive scanning, animage of one frame consists of data that are sampled at the same time.In case of the interlaced scanning, an image of one frame consists ofdata that are sampled at different times, and the samples are alternatedline by line.

The interlaced image of a frame is divided into a top field and a bottomfield. In the interlaced scanning, one frame is divided into two fieldimages. In this specification, an image is treated based on unit ofpicture. A frame or a field may be allocated to the picture.

Three coding methods for an interlaced moving picture are proposed. Afirst coding method is a field picture coding method which performs acoding process, considering each field as an independent picture at apicture or slice level. A second coding method is the frame picturecoding method which performs a coding process after combining two fieldsinto one frame at a picture or slice level. A third coding method is aframe picture coding method with frame/field macroblock, which performsa coding process by combining two fields into one frame and selecting aframe mode or a field mode at a macroblock level.

In the third coding method, two vertically adjacent macroblocks arebound into a pair and the coding is performed in unit of macroblockpair. In FIG. 1, numbers assigned in the macroblock pairs indicatemacroblock addresses that are used to distinguish the macroblocks fromeach other.

Here, frame macroblock is a macroblock which is coded at upper and lowermacroblocks of the macroblock pair in unit of frame. In other words,each macroblock is coded in unit of frame after two fields are combinedinto one frame.

Meanwhile, field macroblock is a macroblock that is coded at upper andlower macroblocks of macroblock pair in unit of field. The macroblockpair is divided into top and independently. At this time, the macroblockpairs are rearranged so that the upper and lower macroblocks mayrespectively contain only top field component and only bottom fieldcomponent. The upper macroblock is called a top field macroblock and thelower macroblock is called a bottom field macroblock.

Reference buffer for storing multiple reference pictures are configuredin unit of frame. In the frame picture coding, all reference picturesare considered as units of frame in which two fields are combined intoone frame, and one picture among the reference frame pictures is usedfor motion compensation. Accordingly, values are allocated to thereference picture indexes in unit of frame.

The reference picture index for P frame is obtained by sorting all thereference frames in an order reverse to a coding order and thensequentially allocating an index, which is increased by one, to thesorted reference frames. The reference picture index for B frame isclassified into list 0 and list 1 and is determined based on a displayorder of the reference frame.

First, in case of the reference frame list 0, indexes are allocated in areverse order to the reference frames whose display order lags behindthe B frame, and then, the remaining indexes are allocated in thedisplay order to the reference frames whose display order leads the Bframe. In case of the reference frame list 1, in contrast to thereference frame list 0, indexes are allocated in the display order tothe reference frames whose display order leads the B frame, and then,the remaining indexes are allocated in a reverse order to the referenceframe whose display order lags behind the B frame. FIG. 2 shows areference picture index for P frame when a size of the reference bufferis 5, and FIG. 3 shows the reference picture index lists 0 and 1 for Bframe.

In the field picture coding, the fields of all reference pictures areconsidered as independent pictures and one of the reference fieldpictures is used for motion compensation. Accordingly, values areallocated to the reference picture indexes in unit of field. At thistime, the reference fields are combined in the unit of frame, and then,the reference picture indexes in each field of the P frame are sorted inan order reverse to a coding order of the frame. Then, index values thatare increased by one are alternately allocated in an order that startsfrom a reference field having parity equal to a current picture to areference field having parity different from the current picture, whilevisiting the sorted reference frames in sequence.

In addition, in case of the reference picture index lists 0 and 1 foreach field of B frame, all the reference fields are combined in unit offrame and then a reference frame is sorted in the same manner as amethod of determining reference frame index of B frame. Thereafter, theindexes that are increased by one are alternately allocated in an orderthat starts from a reference field having parity equal to a currentpicture to a reference field having parity different from the currentpicture, while visiting the sorted reference frames in sequence.

FIG. 4 shows reference picture indexes of top and bottom fields of Pframe when a size of reference buffer is 5, and FIG. 5 shows referencepicture index lists 0 and 1 of top and bottom fields of B frame that canbe used as a reference.

In order to improve coding efficiency, the moving picture coding systemusing multiple reference pictures provides a function of reordering thereference picture indexes before decoding a picture or a slice. It isarbitrarily reordering the reference picture indexes so as to enhancethe coding efficiency after determining initial reference picture indexfor the frame and field pictures. FIG. 6 shows a result of determininginitial reference picture index for P frame and arbitrarily reorderingindexes according to the above-described method.

When the moving picture coding system using the multiple referencepictures codes an interlaced moving picture into a frame picture havingframe/field macroblock, all the reference pictures for the framemacroblock are considered as frame unit and one of the reference framepictures must be used for motion compensation. In addition, and fieldsof all the reference pictures for the field macroblock are considered asindependent pictures and one of the reference field pictures must beused for motion compensation.

Accordingly, in the frame picture coding that selects the frame/fieldcoding modes at the macroblock level, it is necessary to allocate valuesto the reference picture index in frame unit or field unit according tothe coding mode of each macroblock.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method for coding amoving picture that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide a method for coding amoving picture, which efficiently provides reference picture informationused for motion compensation by determining the reference picture indexdifferently according a coding mode of macroblock when interlaced movingpicture is coded with a frame picture having frame/field macroblocks ina moving picture coding system using multiple reference pictures.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription an claim thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, there isprovided a method for coding a moving picture in a moving picture codingsystem using multiple reference picture, a method for setting areference index, when an interlaced moving picture is coded into a framepicture having frame/field macroblock. The method comprising: (a)determining reference picture index of frame unit at a picture (orslice) level; and (b) determining reference picture index according to acoding mode of the macroblock on the basis of the reference pictureindex of frame unit at a macroblock level.

According to another embodiment of the present invention, there isprovided a method for coding an interlaced moving picture into a framepicture having frame/field macroblock in a moving picture coding systemusing multiple reference picture, wherein a reference picture index ofthe frame macroblock is determined at a macroblock level by determiningthe reference picture index of frame unit at a picture (or slice) leveland the reference picture index of frame unit is used.

According to further another embodiment of the present invention, thereis provided a method for coding an interlaced moving picture into aframe picture having frame/field macroblock in a moving picture codingsystem using multiple reference picture, wherein a reference pictureindex of the frame macroblock is determined at a macroblock level bydetermining the reference picture index of frame unit at a picture (orslice) level and respectively allocating a lower index and a higherindex to a top reference field and a bottom reference field whilesequentially visiting the reference frames according to an order ofreference picture index of frame unit, the top and bottom field indexesbeing giving by an equation:top reference field index=2×picture index of reference frame; andbottom reference field index=2×picture index of reference frame+1.

According to further another embodiment of the present invention, thereis provided a method for coding an interlaced moving picture into aframe picture having frame/field macroblock in a moving picture codingsystem using multiple reference picture, wherein a reference pictureindex of the frame macroblock is determined at a macroblock level bydetermining the reference picture index of frame unit at a picture (orslice) level and respectively allocating a lower index and a higherindex to a bottom reference field and a top reference field whilesequentially visiting the reference frames according to an order ofreference picture index of frame unit, the top and bottom referencefield indexes being given by an equation:top reference field index=2×picture index of reference frame+1; andbottom reference field index=2×picture index of reference frame.

According to further another embodiment of the present invention, thereis provided a method for coding an interlaced moving picture into aframe picture having frame/field macroblock in a moving picture codingsystem using multiple reference picture, wherein a reference pictureindex of the frame macroblock is determined at a macroblock level bydetermining the reference picture index of frame unit at a picture (orslice) level and alternately allocating indexes, which are increased byone, to reference fields, starting from a reference field having parityequal to a current field to reference field having parity different fromthe current field while sequentially visiting the reference framesaccording to an order of reference picture index of frame unit in thefield macroblock.

According to further another embodiment of the present invention, thereis provided a method for coding an interlaced moving picture into aframe picture having frame/field macroblock in a moving picture codingsystem using multiple reference picture, wherein a reference pictureindex of the frame macroblock is determined at a macroblock level bydetermining the reference picture index of frame unit at a picture (orslice) level allocating a lower index to a reference field close to acurrent field in view of time and allocating higher index to a referencefield far from the current field in view of time while sequentiallyvisiting the reference frames according to an order of reference pictureindex of frame unit, the indexes of the reference fields being given byan equation:index of the reference field close to the current field=2×picture indexof reference frame; andindex of the reference field far from the current field=2×picture indexof reference frame+1.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 shows macroblock pair in frame picture having general frame/fieldmacroblock;

FIG. 2 shows reference picture indexes of P frame coding in a movingpicture coding system according to the related art;

FIG. 3 shows the reference picture index lists 0 and 1 of B frame codingin a moving picture coding system according to the related art;

FIG. 4 shows reference picture indexes in a coding of top and bottomfields of P frame in a moving picture coding system according to therelated art;

FIG. 5 shows reference picture index lists 0 and 1 in a coding of topand bottom fields of B frame in a moving picture coding system accordingto the related art;

FIG. 6 shows reference picture indexes reordered in a coding of P framein a moving picture coding system according to the related art;

FIG. 7 shows reference picture indexes of P frame and B frame havingframe macroblock in a moving picture coding system according to thepresent invention;

FIG. 8 shows reference picture indexes of P frame and B frame havingfield macroblock in a moving picture coding system according to thepresent invention (case 1);

FIG. 9 shows reference picture indexes of P frame and B frame havingfield macroblock in a moving picture coding system according to thepresent invention (case 2);

FIG. 10 shows reference picture indexes of P frame having fieldmacroblock in a moving picture coding system according to the presentinvention (case 3);

FIG. 11 shows reference picture indexes of B frame having fieldmacroblock in a moving picture coding system according to the presentinvention (case 3); and

FIG. 12 shows reference picture indexes of P frame and B frame havingfield macroblock in a moving picture coding system according to thepresent invention (case 4).

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to accompanying drawings.

When an interlaced moving picture is coded into frame picture havingframe/field macroblock, a moving picture coding system using multiplereference pictures must performs a motion compensation from a referenceframe in order for frame coding in the frame macroblock. In other words,all reference pictures must be considered as frame unit. The movingpicture coding system, however, must performs a motion compensation froma reference field in order for a field coding in the field macroblock.In other words, all reference pictures must be considered as field unit.

Accordingly, the frame pictures having frame/field macroblock must useindexes having different structures at macroblock level. For example,the frame macroblock uses a reference picture index of frame unit andthe field macroblock uses a reference picture index of field unit. Itshould be considered that the reference picture indexes can be reorderedat a picture or slice level.

Therefore, the frame picture having frame/field macroblocks shouldconsider the reference picture in frame unit at a picture or slice leveland have the reordered reference picture indexes of frame unit. It isnecessary to determine reference picture index according to a codingmode of macroblock based on the reference picture indexes of the frameunit at the macroblock level.

The present invention provides a method for determining referencepicture index in frame picture having frame/field macroblock. The methodincludes a process of determining reference picture index at a picture(or slice) level and a process of determining reference picture index ata macroblock level.

[1] Determination of Reference Picture Index at Picture (or Slice) Level

All the reference pictures are considered in frame unit at a picture orslice level and reference picture indexes of frame unit are calculated.

In the method or determining a reference picture index for P frame,reference frames are sorted in an order reverse to a coding order andindexes are allocated while visiting the sorted reference frames insequence.

Reference picture indexes for B frame are determined based on a displayorder of the reference frames. First, in case of a reference frame list0, indexes are allocated in a reverse order to reference frames whosedisplay orders lag behind the B frame and the remaining indexes areallocated in the display order to reference frames whose display orderlead the B frame.

In case of a reference frame list 1, in contrast to the reference framelist 0, indexes are allocated in the display order to reference frameswhose display orders are higher than the B frame and the remainingindexes are allocated in a reverse order to reference frames whosedisplay orders are lower than the B frame. When the reference pictureindexes are reordered so as to enhance a coding efficiency, thereference picture indexes of frame unit are reordered.

[2] Determination of Reference Picture Index at Macroblock Level

The reference picture index is modified according to the coding mode ofthe macroblock while performing a coding in unit of macroblock pair withrespect to the reference picture indexes of frame unit, which areobtained at the picture (or slice) level. This process will be describedbelow.

[2.1] Case of Frame Macroblock

Since motion compensation must be performed to frame macroblocks fromreference frame, the reference picture index should be frame unit.Accordingly, the reference picture indexes of frame unit, which areobtained at the picture (or slice) level, are used.

Reference frame stored in a reference buffer should be configured withfield pair having parities opposite to each other. FIG. 7 showsreference picture indexes for frame macroblock in P frame and B framewhen a size of the reference buffer is 5.

[2.2] Case of Field Macroblock

Since motion compensation must be performed to field macroblocks fromreference field, the reference picture index should be field unit. Inthis case, field pair having parities opposite to each other is alsopresent in the reference buffer. Accordingly, each reference frame isdivided into two fields while sequentially visiting the reference frameaccording to the reference picture indexes of frame unit, which areobtained at the picture (or slice) level. Then, the reference pictureindexes are newly allocated to each field. The reference picture indexesfor two fields of each reference frame are allocated in various methods(Cases 1 to 4).

(Case 1)

Regardless of the top and bottom field macroblocks of a current fieldmacroblock, a lower index is allocated to the top reference field and ahigher index is allocated to the bottom reference field whilesequentially visiting the reference frames in an order of the referencepicture indexes, which are obtained at the picture (or slice) level.

In other words, the top and bottom reference field indexes can be givenby an equation below.Top reference field index=2×picture index of reference frameBottom reference field index=2×picture index of reference frame+1

FIG. 8 shows reference picture indexes for field macroblocks of P frameand B frame.

(Case 2)

Regardless of the top and bottom field macroblocks of a current fieldmacroblock, a lower index is allocated to the bottom reference field anda higher index is allocated to the top reference field whilesequentially visiting the reference frames in an order of the referencepicture indexes, which are obtained at the picture (or slice) level.

In other words, the top and bottom reference field indexes can be givenby an equation below.Top reference field index=2×picture index of reference frame+1Bottom reference field index=2×picture index of reference frame

FIG. 9 shows reference picture indexes for field macroblocks of P frameand B frame.

(Case 3)

Indexes that are increased by one are alternately allocated to referencefields, starting from the reference field having a parity equal to thecurrent field to the reference field having a parity different from thecurrent field, while sequentially visiting the reference framesaccording to a reference picture index order of the picture (or slice)level. FIGS. 10 and 11 show reference picture indexes for the fieldmacroblocks of P frame and B frame.

(Case 4)

Regardless of the top and bottom field macroblocks of a current fieldmacroblock, a lower index is allocated to reference field close to thecurrent field in view of time and a higher index is allocated toreference field far from the current field in view of time whilesequentially visiting the reference frames in an order of the referencepicture indexes of the picture (or slice) level.

In other words, the reference field indexes can be given by an equationbelow.Reference field index close to the current field=2×picture index ofreference frameReference field index far from the current field=2×picture index ofreference frame+1

In FIG. 12, there are shown reference picture indexes for fieldmacroblock of P frame and B frame.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

According to a coding a moving picture method of the present invention,when a moving picture coding system using multiple reference picturescodes an interlaced moving picture into a frame picture havingframe/field macroblock, the moving picture coding system efficientlyprovides reference picture information used for motion compensation bydifferently determining reference picture index according to codingmodes of macroblocks.

1. A method of selecting a reference picture for processing a fieldmacroblock, comprising: selecting at least one reference picture forprocessing a field macroblock from at least one reference picture listusing reference picture index information, each selected at least onereference picture being a field.
 2. The method of claim 1, furthercomprising: processing the field macroblock using the selected at leastone reference picture.
 3. The method of claim 1, wherein the referencefield is one of a top field and a bottom field.
 4. The method of claim1, further comprising: forming the at least one reference picture list.5. The method of claim 4, wherein the forming step comprises:initializing the at least one reference picture list; and reordering theat least one reference picture list.
 6. The method of claim 1, whereineach selected at least one reference picture is a field of a referenceframe.
 7. The method of claim 1, wherein if the reference picture indexinformation is an even index number, then the selected at least onereference field has a same field parity as the field macroblock.
 8. Themethod of claim 7, wherein if the reference picture index information isan odd index number, then the selected at least one reference field hasa field parity different from the field macroblock.
 9. The method ofclaim 1, wherein if the reference picture index information is an oddindex number, then the selected at least one reference field has a fieldparity different from the field macroblock.
 10. The method of claim 1,wherein if the reference picture index information is an even indexnumber and the field macroblock is a top field macroblock, then theselected at least one reference field is a top field.
 11. The method ofclaim 1, wherein if the reference picture index information is an evenindex number and the field macroblock is a bottom field macroblock, thenthe selected at least one reference field is a bottom field.
 12. Themethod of claim 1, wherein if the reference picture index information isan odd index number and the field macroblock is a top field macroblock,then the selected at least one reference field is a bottom field. 13.The method of claim 1, wherein if the reference picture indexinformation is an odd index number and the field macroblock is a bottomfield macroblock, then the selected at least one reference field is atop field. 14-21. (canceled)